Tires for use on automobiles, trucks, and similar vehicles are made of vulcanized rubber that is formed to be mounted on a wheel that includes a tire-retaining rim. Such wheels conventionally are made from one or more pieces of metal, and may be cast or assembled from cast parts. Depending upon the metal that is used to make the wheel, parts of the wheel may also be extruded and/or fabricated into the desired shapes for assembly as by, for example, welding.
Automobiles designed for racing are weight-sensitive, and therefore it has been desirable to use wheels made from light metals, such as magnesium. aluminum, and alloys of those and other elements. Such alloys are particularly desirable when they permit easy fabrication as a result of ductile properties, yet at the same time impart structural strength to support the heavy loads endured by the wheels without requiring otherwise unnecessary quantities of metal to form rigid structural members. These same concerns have increasingly been present in conventional automobiles designed for consumer applications, and for trucks and other vehicles, because of demands for fuel efficiency, requiring lighter-weight vehicles.
Also of concern to the automobile industry is the desire to use a lesser quantity of metals and alloys in each part of the automobile to reduce costs. That industry has sought to use such materials in a manner that minimizes the number of steps, and the amount of energy, employed in the manufacturing process, thereby to reduce costs. In addition, manufacturing that reduces waste products is particularly desirable since it minimizes environmental degradation resulting from the manufacturing process.
To that end, several lightweight wheels have been proposed. These include Ridout, U.S. Pat. No. 4,345,360, Martenet, U.S. Pat. No. 2,992,045, Brown, U. S. Pat. No. 4,693,520, Walther, U.S. Pat. No. 4,624,038, Zulauf, U.S. Pat. No. 4,487,456, Lester et al., U.S. Pat. No. 4,256,348, and Schmidt, U.S. Pat. No. 4,190,297. Some of the disadvantages of the wheels described in these patents are set forth below.
Ridout discloses a wheel made from a magnesium-silicon alloy of aluminum that is extruded to form a rim. That rim includes a flange that is later roll-pressed to form a wheel "center" for joining the wheel to a hub and axle in an automobile or other vehicle. The process for making the rim disclosed by Ridout includes the step of expanding the rim to the desired size, which precludes use of many lighter-weight, magnesium-based alloys that cannot be expanded following extrusion.
Martenet discloses an extruded wheel rim that includes a hollow section, or cross-piece, extruded integrally with the rim to absorb the maximum load when the tire and wheel are in service. The inclusion of one or more such cross-pieces undesirably adds to the weight of the wheel.
Zulauf relates to a process of using the wheel rim as a mold to form a portion of the wheel body in an aluminum, steel or magnesium wheel, thereby reducing the number of steps required to manufacture the wheel and reducing the likelihood that the wheel will not be true at the end of the manufacturing process. The process disclosed in Zulauf, however, is unduly labor intensive because it requires a precise setup to construct a mold using the wheel rim, among other disadvantages.
Walther relates to a vehicle wheel made from an aluminum or magnesium alloy that is cast to form a rim and then shear-formed into the desired rim configuration, reducing the thickness of the rim and also its strength. The casting process requires additional steps to finish the rim by removing undesirable surface elements and residue from casting that may disrupt the roll-forming process or adversely affect the integrity of a tire placed onto the rim.
Brown discloses a wheel fabricated from aluminum, steel or magnesium, and alloys thereof, that uses detachable spokes in order to provide the option of reducing the wheel weight. The wheel itself is preferably cast, but may be forged, extruded or spun into the appropriate shape, and includes a flange or center that is bolted on. The use of bolt construction adds steps to the fabrication process, increasing both the margin for error and the cost of manufacturing. That construction also undesirably adds to the weight of the finished wheel.
Schmidt relates to a wheel rim made from an extruded alloy of aluminum or magnesium that is reinforced by a circumferential steel strip. Thus, according to Schmidt, it is desirable to add the step of embedding (as by welding) a strip of a higher strength metal to a lower strength, light-weight metal. That, however, undesirably adds to both the manufacturing costs and the weight of the finished wheel.
Lester relates to a wheel for use in a motorcycle that is made from an extruded rim section that is elongated beyond its yield point prior to fabrication into the desired configuration. Thereafter, the expanded wheel is further stretched by 2-3% and joined to a center, around which the rim is compressed to fit.
Even these designs, however, have not satisfied the demand in the marketplace for lightweight wheels that are both strong and inexpensive to produce, because of the problems identified.